FIGS. 1 and 2 depict a conventional diaphragm valve 10. The valve 10 generally includes a valve body 12 defining a fluid flow passageway 14. A weir 16, which also referred to in the art as a valve seat, is positioned within the fluid passageway 14 for cooperating with a diaphragm 18 to control the flow of fluid through the fluid passageway 14. In the fully open configuration depicted in FIG. 1, the distance separating the diaphragm 18 and the weir 16 is at its maximum to permit fluid flow through the valve. In the closed configuration depicted in FIG. 2, the diaphragm 18 bears on the weir 16 to prevent fluid flow through the valve 10.
A bonnet assembly 20 is mounted to an opening 22 defined in the valve body 12. The bonnet assembly 20 generally includes a housing 21 and a threaded valve stem 24 threadedly engaged with a threaded hole provided in the housing 21. A compressor 26 is retained on one end of the valve stem 24, and a handwheel 28 is mounted to the opposite end of the valve stem 24.
A tube nut 32 is captivated between the valve stem 24 and the compressor 26. A threaded stud 30 is provided on the top side 23 of the diaphragm 18 for threaded coupling with a threaded aperture that is formed in the tube nut 32. The threaded stud 32 passes through a hole disposed in a backing cushion 37. The backing cushion 37 is sandwiched between the diaphragm 18 and a flange 31 of the bonnet housing 21.
The handwheel 28 is rotatably coupled to an opposing end of the valve stem 24 for rotating the valve stem 24 to translate the central portions of the diaphragm 18 and the backing cushion 37 in either an upward or downward direction with respect to the weir 16 for either restricting or permitting fluid flow through the valve 10.
The diaphragm 18 and the backing cushion 37 are sandwiched together between the flanges of the valve body 12 and the bonnet 20. A set of bolts 38 join valve body 12 and the bonnet 20 together and maintain the diaphragm 18 and the backing cushion 37 in a state of compression to create a fluid tight seal at the interface between the flange 39 of the valve body 12 and the diaphragm 18. The diaphragm 18, which is composed of plastic, includes a circumferential sealing gland 33 that is positioned in contact with the flange 39 of the valve body 12.
The fluid-tight seal maintained between the flange 39 of the valve body 12 and the diaphragm 18 may be commonly referred to in the art as a perimeter seal. Ordinarily, the strain energy of the backing cushion 37 maintains adequate sealing pressure at the perimeter seal. Conventional backing cushions, which are composed of rubber or other elastomeric material, deteriorate over time due to thermal cycling. As the backing cushion deteriorates, the pressure exerted by the diaphragm against the valve body decreases, thereby increasing the potential for either fluid leakage at the perimeter seal or the introduction of contaminants into the valve through the perimeter seal. Accordingly, there exists a need to improve upon the sealing performance of a diaphragm valve at the perimeter seal.